Devices with strained isolation features

ABSTRACT

A semiconductor device and a method of forming the same are provided. A semiconductor device of the present disclosure includes a first fin including a first source/drain region, a second fin including a second source/drain region, a first isolation layer disposed between the first source/drain region and the second source/drain region, and a second isolation layer disposed over the first isolation layer. A first portion of the first isolation layer is disposed on sidewalls of the first source/drain region and a second portion of the first isolation layer is disposed on sidewalls of the second source/drain region. A portion of the second isolation layer is disposed between the first portion and second portion of the first isolation layer.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs.

However, such scaling down has also increased the complexity ofprocessing and manufacturing ICs and, for these advances to be realized,similar developments in IC processing and manufacturing are needed. Forexample, a three-dimensional transistor, such as a fin-like field-effecttransistor (FinFET), has been introduced to replace a planar transistor.A typical FinFET is fabricated with a thin “fin” (or fin structure)extending up from a substrate. The channel of the FET is formed in thisvertical fin, and a gate is provided over (e.g., wrapping around) thechannel region of the fin. Wrapping the gate around the fin increasesthe contact area between the channel region and the gate and allows thegate to control the channel from multiple sides. This can be leveragedin a number of ways, and in some applications, FinFETs provide reducedshort channel effects, reduced leakage, and higher current flow. Inother words, they may be faster, smaller, and more efficient than planardevices.

FinFETs may include stressor structures that exert stress on channelregions of fins in order to improve performance thereof by increasingelectron mobility or hole mobility in these channel regions. Whileconventional stressor structures are generally adequate for theirintended purposes, they have not been entirely satisfactory in allrespects. For example, some of the stressor structures may undergostress relaxation and become less effective in exerting stress on thechannel regions.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion. It is also emphasized that thedrawings appended illustrate only typical embodiments of this inventionand are therefore not to be considered limiting in scope, for theinvention may apply equally well to other embodiments.

FIG. 1 is a flow diagram of a method for fabricating a semiconductordevice according to various aspects of the present disclosure.

FIG. 2 is a perspective diagrammatic view of a workpiece according tovarious aspects of the present disclosure.

FIGS. 3-8 are fragmentary cross-sectional diagrammatic views of aworkpiece at various fabrication stages of a method, such as the methodin FIG. 1, according to various aspects of the present disclosure.

FIG. 9 is a chart showing drive current performance gain in an n-typeFinFET in relation to a recess depth into shallow trench isolation(STI), according to various aspects of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Still further, when a number or a range of numbers is described with“about,” “approximate,” and the like, the term is intended to encompassnumbers that are within a reasonable range including the numberdescribed, such as within +/−10% of the number described or other valuesas understood by person skilled in the art. For example, the term “about5 nm” encompasses the dimension range from 4.5 nm to 5.5 nm.

The present disclosure is directed to, but not otherwise limited to, astressor structure that exerts stress on channel regions of FinFETs toimprove device performance. In particular, the present disclosure isdirected to an isolation structure that exerts tensile stress on channelregions of FinFETs in an n-type device region to increase electronmobility therein. In some embodiments, the isolation structure includesa first isolation layer having a recess and a second isolation layerdisposed over the first isolation layer and within the recess in thefirst isolation layer. The isolation structure is disposed aroundsource/drain regions of n-type FinFETs. After compressive strain isinduced in the second isolation layer that wraps around the finstructures, tensile stress exerted on the source/drain regions mayresult in tensile stress on the channel regions adjacent thesource/drain regions.

To illustrate the various aspects of the present disclosure, a FinFETfabrication process is discussed below as an example. In that regard,the FinFET device has been gaining popularity in the semiconductorindustry. The FinFET device may be a complementarymetal-oxide-semiconductor (CMOS) device including a P-typemetal-oxide-semiconductor (PMOS) FinFET device and an N-typemetal-oxide-semiconductor (NMOS) FinFET device. The following disclosurewill continue with one or more FinFET examples to illustrate variousembodiments of the present disclosure, but it is understood that theapplication is not limited to the FinFET device, except as specificallyclaimed.

FIG. 1 illustrates a flow chart of a method 100 for fabricating asemiconductor device. At block 102 of the method 100, a workpiece isprovided. The workpiece includes a fin in a first isolation layer. Atblock 104 of the method 100, a source/drain feature is formed over asource/drain region of the fin. At block 106 of the method 100, thefirst isolation layer is recessed. At block 108 of the method 100, anetch stop layer is deposited over the recessed first isolation layer andthe source/drain feature. At block 110 of the method 100, a secondisolation layer is formed over the etch stop layer. At block 112 of themethod 100, the second isolation layer is annealed. At block 114 of themethod 100, further processes may be performed to complete fabricationof the semiconductor device. While operations in method 100 are labeledusing reference numerals in a substantially sequential order, thepresent disclosure is not so limited and the method 100 may includevarious embodiment. Unless otherwise specified herein, additional stepscan be provided before, during, and after the method 100, and some ofthe steps described can be replaced or eliminated for other embodimentsof the method 100.

Blocks of the method 100 in FIG. 1 may be better described inconjunction with FIGS. 2-8. Referring now to FIGS. 1 and 2, the method100 include a block 102 where a workpiece 200 is provided. FIG. 2 is aperspective diagrammatic view of the workpiece 200, according to someembodiments of the present disclosure. The workpiece 200 can be includedin a microprocessor, a memory, and/or other IC device. In someimplementations, workpiece 200 is a portion of an IC chip, a system onchip (SoC), or portion thereof, that includes various passive and activemicroelectronic devices, such as resistors, capacitors, inductors,diodes, p-type field effect transistors (PFETs), N-type field effecttransistors (NFETs), metal-oxide semiconductor field effect transistors(MOSFETs), complementary metal-oxide semiconductor (CMOS) transistors,bipolar junction transistors (BJTs), laterally diffused MOS (LDMOS)transistors, high voltage transistors, high frequency transistors, othersuitable components, or combinations thereof. The transistors may beplanar transistors or non-planar transistors, such as fin-like FETs(FinFETs) or gate-all-around (GAA) transistors. FIGS. 3-8 arefragmentary cross-sectional diagrammatic views along section A-A′ of aworkpiece 200 at various fabrication stages of a method of the presentdisclosure, such as method 100 of FIG. 1. FIGS. 2-8 have been simplifiedfor the sake of clarity to better understand the inventive concepts ofthe present disclosure. Additional features can be added in workpiece200, and some of the features described below can be replaced, modified,or eliminated in other embodiments of workpiece 200.

The workpiece 200 includes a substrate 202. The substrate 202 may bemade of silicon or other semiconductor materials. Alternatively oradditionally, the substrate 202 may include other elementarysemiconductor materials such as germanium. In some embodiments, thesubstrate 202 is made of a compound semiconductor such as siliconcarbide, gallium arsenic, indium arsenide, or indium phosphide. In someembodiments, the substrate 202 is made of an alloy semiconductor such assilicon germanium, silicon germanium carbide, gallium arsenic phosphide,or gallium indium phosphide. In some embodiments, the substrate 202includes an epitaxial layer. For example, the substrate 202 may includeone or more epitaxial layers overlying a bulk semiconductor.

The workpiece 200 also includes one or more fin structures 204 (e.g., Sifins or fins) that extend from the substrate 202 in the Z-direction. Thefin structures 204 extend or are elongated along the X-direction and mayoptionally include germanium (Ge). The fin structures 204 may be formedby using suitable processes such as photolithography and etchingprocesses. In some embodiments, the fin structure 204 is etched from thesubstrate 202 using dry etch or plasma processes. In some otherembodiments, the fin structure 204 can be formed by a double-patterninglithography (DPL) process, a quadruple-patterning lithography (QPL)process or a multiple-patterning lithography (MPL) process. Generally,DPL, QPL and MPL processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process.

A first isolation layer 206, such as a shallow trench isolation (STI)structure, is formed to surround and among the fin structures 204 suchthat a lower portion 204L of the fin structure 204 iscovered/buried/embedded in the first isolation layer 206 and an upperportion 204U that protrudes from and above the first isolation layer206. The upper portion 204U is smaller than the lower portion 204L. Insome embodiments, a height of the upper portion 204U measured from thesubstrate is between about 2 nm and about 20 nm and a height of thelower portion 204L measured from the substrate is between about 20 nmand about nm. In those embodiments, the height of the upper portion 204Uis between about 5% and about 50% of the height of the lower portion204L. The first isolation layer 206 may also be referred to as STI 206.As shown in FIG. 2, the first isolation layer 206 is on top surfaces ofthe substrate 202 and in direct contact with sidewalls of the lowerportion 204L of the fin structure 204. Each of the fin structures 204may include a channel region 207 and a source/drain region 209 adjacentthe channel region 207. In some embodiments illustrated in FIG. 2, oneor more gate structures 214 may be formed over and around the channelregion(s) 207 and the source/drain features 210 may be formed over andaround the source/drain region(s) 209. The first isolation layer 206prevents electrical interference or crosstalk and may be referred to asSTI 206.

Depending on the process, the gate structure 214 may be a dummy gatestructure (or placeholder gate structure) or a functional metal gatestructure. When the gate structure 214 is a dummy gate structure in agate-last process, the workpiece 200 may include a dummy gate dielectriclayer 212 between the gate structure 214 and the fin structures 204. Inthe gate-last process, the dummy gate structure and the dummy gatedielectric layer will be replaced with a gate dielectric layer and ametal gate structure. When the gate structure 214 is a functional gatestructure in a gate-first process, the workpiece 200 may include a gatedielectric layer between the gate structure 214 and the fin structures204. The gate structure 214 may include polysilicon when it is a dummygate structure or metal (or metal nitride) when it is a functional metalgate structure. Such metal (or metal nitride) includes tantalum nitride(TaN), nickel silicide (NiSi), cobalt silicide (CoSi), molybdenum (Mo),copper (Cu), tungsten (W), aluminum (Al), nickel (Ni), cobalt (Co),zirconium (Zr), platinum (Pt), ruthenium (Ru), or other applicablematerials.

The gate dielectric layer may include dielectric materials, such assilicon oxide, silicon nitride, silicon oxynitride, dielectricmaterial(s) with high dielectric constant (high-k), or combinationsthereof. Examples of high-k dielectric materials include hafnium oxide,zirconium oxide, aluminum oxide, hafnium dioxide-alumina alloy, hafniumsilicon oxide, hafnium silicon oxynitride, hafnium tantalum oxide,hafnium titanium oxide, hafnium zirconium oxide, the like, orcombinations thereof. In some embodiments, the gate structure 214includes additional layers, such as interfacial layers, capping layers,diffusion/barrier layers, or other applicable layers.

The gate structure 214 may be formed by a deposition process, aphotolithography process and an etching process. The deposition processincludes chemical vapor deposition (CVD), physical vapor deposition(PVD), atomic layer deposition (ALD), high density plasma CVD (HDPCVD),metal organic CVD (MOCVD), remote plasma CVD (RPCVD), plasma enhancedCVD (PECVD), plating, other suitable methods, and/or combinationsthereof. The photolithography processes include photoresist coating(e.g., spin-on coating), soft baking, mask aligning, exposure,post-exposure baking, developing the photoresist, rinsing, drying (e.g.,hard baking). The etching process includes a dry etching process or awet etching process. Alternatively, the photolithography process isimplemented or replaced by other proper methods such as masklessphotolithography, electron-beam writing, and ion-beam writing.

In some embodiments, the gate structures 214 may include one or morespacers. In some embodiments, the gate structures 214 are first formedover the channel region 207 of the fins 204 before the source/drainfeatures 210 are formed. After the gate structures 214, which may bedummy gate structures, are formed, one or more spacer layers are thendeposited over the workpiece 200 to cover the gate structures 214 andthe source/drain region 209 of the fin structure. In some embodiments,the one or more spacers may include a spacer 208 disposed over thesidewalls of the fin structures 204. In the embodiments represented inFIG. 2, after the one or more spacers are deposited, the source/drainregion 209 of the fin structure 204 are recessed ahead of the epitaxyprocess for formation the source/drain features 210. In thoseembodiments, the spacer 208 is recessed such that it covers sidewalls ofthe upper portion 204U of the fin structure 204. Because the epitaxyprocess to form the source/drain features 210 only forms epitaxy on thefin structure 204, the spacer 208 allows the source/drain feature 210 tobe vertically spaced apart along the Z direction from a top surface ofthe first isolation layer 206.

The one or more spacers, including the spacer 208, may include silicon,oxygen, nitrogen, and/or carbon and may be silicon oxide, siliconnitride, silicon oxynitride, or silicon oxycarbonitride, siliconcarbonitride. In some embodiments, the spacer 208 and the firstisolation layer 206 may be formed of different dielectric materials toexperience different etching rate when etched by the same etchant. Forexample, the spacer 208 may be formed of silicon nitride while the firstisolation layer 206 is formed of silicon oxide. In that example, thefirst isolation layer 206 may be selectively etched while the spacer 208is substantially unetched. In that regard, the spacer 208 may serve asan etch mask or an etch stop layer for the etching/recessing of thefirst isolation layer 206 disposed directly under the spacer 208.

Referring now to FIGS. 1, 2 and 3, the method 100 includes a block 104where the source/drain feature 210 is formed over the source/drainregion 209 of the fin structure 204. In is noted that while notspecifically shown, the workpiece 200 includes an n-type device regionand a p-type device region and each of the n-type and p-type deviceregions includes one or more fin structures 204. In some embodiments,FIGS. 3-7 illustrate only the n-type device region, which may or may notbe formed adjacent a p-type device region; and FIG. 8 illustratessource/drain regions of both the n-type device region and the p-typedevice region. In some embodiments, the source/drain features 210 overthe n-type device region and the source/drain features over the p-typedevice region are formed separately. For example, a hard mask layer isfirst deposited using CVD, ALD, spin-on coating, or other suitabledeposition techniques in a blanket manner over the workpiece 200,including over the n-type device region and the p-type device region.The hard mask is then patterned using photolithography techniques. Forinstance, a photoresist layer, which may include multiple materiallayers, may be deposited over the hard mask. The photoresist layer isthen exposed to radiation reflected from or going through a patternedmask. After being subject to a post-exposure bake, the exposedphotoresist layer may undergo chemical changes that allow the exposed orthe unexposed portions of the photoresist layer to be removed by adeveloper to form a patterned photoresist layer. The hard mask, which isnot masked by the patterned photoresist layer is then removed to form apatterned hard mask that exposes source/drain regions of one of thedevice regions. Similar processes are then repeated to form anotherpatterned hard mask that exposes source/drain regions of the otherdevice region. Separately forming n-type source/drain features andp-type source/drain features allows for individualized performancetuning by applying different epitaxial compositions, different dopantconcentrations, different dopant species, different stressor structuresto source/drain features of different types. In some embodiments,operations of method 100 of the present disclosure are only applied ton-type device regions to form a stressor structure that boostsperformance of the n-type devices.

Referring now to FIGS. 1 and 4, the method 100 includes a block 106where the first isolation layer 206 is recessed to form recessed firstisolation layer 206′. In some embodiments, a portion of the firstisolation layer 206 that is not covered by the spacer 208 isanisotropically and selectively etched to form a recess 2060. Asillustrated in FIG. 4, the recess 2060 extends between two neighboringfin structures 204. The recessed first isolation layer 206′ may bedivided into two wall portions 2061 and 2062 that are disposed oversidewalls the lower portion 204L of the fins 204 and a bottom portion2063 extending between the two wall portions 2061 and 2062. In someembodiments, the recessing at block 106 is performed using a chemistrythat etches the first isolation layer 206 faster than it etches thespacer 208 and the source/drain feature 210. In some implementations,the recessing at block 106 may be a dry etch, a wet eth, or acombination thereof. It is noted that the first isolation layer 206 isnot etched through at block 106 to expose either the substrate 202 orthe fin structures 204 to prevent formation of any defects or leakpaths. In this regard, the first spacer layer 206 has a first thicknessT1 before block 106 and the recessed first spacer layer 206′ has asecond thickness T2 after block 106. In some instances, the secondthickness T2 is about 5% and about 50% of the first thickness T1. Eachof the two wall portions 2061 and 2062 may have a third thickness T3. Insome instances, the third thickness T3 is about 1 nm and about 15 nm. Asillustrated in FIG. 4, when viewed along the Y direction, the two wallportions 2061 and 2062 on both sides of the bottom portion 2063 riseabove a top surface of the bottom portion 2063 along the Z direction,giving the recessed first isolation layer 206′ a shape of the letter “U”or a U-shape. In other words, the surface of the bottom portion 2063 islower than top surfaces of the two wall portions 2061 and 2062 along theZ direction.

Referring now to FIGS. 1 and 5, the method 100 includes a block 108where an etch stop layer 216 is deposited over the recessed firstisolation layer 206′ and the source/drain feature 210. In someembodiments, the etch stop layer 216 may be formed of silicon nitride,silicon oxycarbonitride, silicon oxycarbide, or other suitabledielectric material. In some implementations, the etch stop layer 216has a different etching selectivity from the second isolation layer 218to be deposited at block 110. As such, the etch stop layer 216 may slowdown the etching process through the second isolation layer 218 when asource/drain contact via opening is to be formed through the secondisolation layer 218. In some instances, the etch stop layer 216 may alsobe referred to as a contact etch stop layer 216 or CESL 216.

Referring now to FIGS. 1 and 6, the method 100 includes a block 110where a second isolation layer 218 is formed over the etch stop layer216. In some embodiments, the second isolation layer 218 has acomposition that is different from the composition of the firstisolation layer 206. In some implementations, the second isolation layer218 may be formed using CVD, ALD, or other suitable depositiontechnique. In some instances, the second isolation layer 218 may beformed of a dielectric material that will shrink or condense in ananneal process. For example, some functional groups of the dielectricmaterial may decompose or condense to produce volatile compounds thatwill leave the dielectric material. In some embodiments, the secondisolation layer 218 may be formed of silicon oxide, silicon nitride,silicon oxynitride, silicon carbide, other suitable low-k materials. Asillustrated in FIG. 6, a portion of the second isolation layer 218 isdeposited within the recess 2060 that is lined by the etch stop layer216 such that the etch stop layer 216 is disposed between the recessedfirst isolation layer 206′ and the second isolation layer 218. Inaddition, in embodiments represented in FIG. 6, the lower portions 204Lof two neighboring fin structures 204 are separated by two wall portions2061 and 2062, two layers the etch stop layer 216, and the portion ofthe second isolation layer 218 that is deposited within and extends intothe recess 2060. When the thickness of the recessed first isolationlayer 206′, such as the second thickness T2 and the third thickness T3,is minimized, the volume/thickness of the second isolation layer 218that surrounds the fin structures 204 may be maximized. The maximizationof the volume/thickness of the second isolation layer 218 maximizes thesize of the structure that exerts stress on the fin structure 204,including the channel region 207 of the fin structure 204. After thesecond isolation layer 218 is deposited, a planarization process, suchas a chemical mechanical process (CMP), may be performed to planarizethe top surface of the second isolation layer 218. In this regard, thesecond isolation layer 218 may function as an interlayer dielectric(ILD) layer of an interconnect structure that includes multiple ILDlayers, metal lines, and contact vias.

Referring now to FIGS. 1 and 7, the method 100 includes a block 112where the second isolation layer 218 is annealed using an annealingprocess 300. In some embodiments, the workpiece 200 is annealed betweenabout 500° C. and about 1200° C. to compressively strain the secondisolation layer 218. The annealing process 300 may include a furnaceannealing process, a rapid thermal annealing (RTA) process, a spikeannealing process, a laser annealing process, or a combination thereof.Depending on the type of annealing technique used, the anneal process300 may include different anneal times. In cases where the annealprocess 300 is performed using a furnace annealing process, the annealtime may be between about 10 mins and about 5 hours. When an RTAprocess, a spike annealing process, or a rapid thermal annealing processis used, the anneal time may be measured with nano-seconds or seconds.In some implementations, the second isolation layer 218 includes one ormore types of functional groups that may decompose or undergocondensation reactions during the annealing process 300 to produce avolatile compound that can be removed from the second isolation layer218. Such functional groups may be referred to as leaving groups. Oncethe leaving groups leave the second isolation layer 218, the secondisolation layer 218 may shrink in volume or become densified. Theshrunken second isolation layer 218 is compressively strained and mayexert a tensile stress on the features around it, including on the finstructure 204 wrapped around by the second isolation layer 218. Theshrunken second isolation layer 218 may also exert a tensile stress onthe channel region 207 of the fin structure 204 and such tensile stresshas been observed to improve the performance of n-type devices due toincreased electron mobility. In some other implementations, the secondisolation layer 218 does not include any leaving group and the annealprocess 300 may bring about desorption, bond formations, or bondrearrangements to compressively strain the second isolation layer 218.Some conventional techniques include utilizing the first isolation layer206 as a compressively strained stressor structure. However, as thefirst isolation layer 206 is formed early in the process and has toendure much of the fabrication process, the compressive strain in thefirst isolation layer 206 may be relaxed in the process, making thefirst isolation layer 206 a less effective stressor structure. Unlikethe first isolation layer 206, the second isolation layer 218 isdeposited later in the process in an intentionally enlarged space tomaximize its effectiveness as a stressor structure for improvedperformance.

Referring to FIGS. 1 and 8, the method 100 includes a block 114 wherefurther processes are performed. Such further processes may include, forexample, processes for forming the source/drain features in the p-typedevice region. For ease of comparison, cross-sectional diagrammaticviews of source/drain regions of an n-type device region 1000 and ap-type device region 2000 are illustrated in FIG. 8. In someembodiments, after the source/drain features 210 in the n-type deviceregion 1000 have been formed, another hard mask is deposited over theworkpiece 200 and is patterned to expose the source/drain regions in thep-type device region 2000, while covering the rest of the workpiece 200.Unlike the n-type device region 1000 illustrated on the left-hand side,the first isolation layer 206 in the p-type device region 2000 is notrecessed and its top surface remains planar and substantially parallelto the top surface of the substrate 202. That is, when view along the Ydirection, the first isolation layer 206 in the p-type device region2000 is not U-shaped like the recessed first isolation layer 206′ in then-type device region 1000. The source/drain feature in the p-type deviceregion 2000 is denoted differently as 211 as it has a differentepitaxial composition from that of the source/drain feature 210 in then-type device region 1000. Similar to the n-type device region 1000, thep-type device region 2000 includes the etch stop layer 216 that isdeposited over the first isolation layer 206, the spacer 208, and thesource/drain feature 211. Due to the absence of the recess in the firstisolation layer 206, an ILD layer 219 deposited in the p-type deviceregion 2000 does not extend into the first isolation layer 206. In someembodiments, the ILD layer 219 has a composition that is different fromthe composition of the second isolation layer 218 and ILD layer 219 andis not intentionally designed to exert tensile stress on the finstructures 204 thereunder. For example, the ILD layer 219 may be formedof a material that neither includes any leaving group that may leave theILD layer 219 nor densifies when it undergoes an annealing process. Insome implementations, the ILD layer 219 may include silicon oxide,silicon nitride, silicon oxynitride, silicon oxycarbonitride, or siliconoxycarbide, or other suitable materials. To summarize, in someembodiments, the formation of the source/drain feature 211 in the p-typedevice region 2000 may not include any operations comparable to those inblocks 106 and 112 in method 100 of FIG. 1.

Such further processes may also include processes for formingsource/drain contacts 220 illustrated in FIG. 8. In some embodiments,source/drain contact openings are first formed through the secondisolation layer 218 in the n-type device region 1000 or the ILD layer219 in the p-type device region 2000. Thereafter, a metal-containingbarrier layer 222, such as tantalum nitride or titanium nitride,tungsten nitride, or cobalt nitride, may be deposited within thesource/drain contact openings. The barrier layer 222 serves to preventoxidation of source/drain contacts 220 due to oxygen diffusion from thesecond isolation layer 218 or the ILD layer 219. In someimplementations, the workpiece 200 is then annealed to promote reactionbetween the source/drain features 210/211, on the one hand, and thebarrier layer 222, on the other, to form a silicide layer 224 at theinterface of the source/drain feature 210/211 and the barrier layer 222.In some instances, the barrier layer 222 that remains over the silicidelayer 224 may be removed using a suitable etching technique so as toreduce contact resistance. A metal fill layer 226 may then be depositedto fill the source/drain contact opening to form the source/draincontact 220. A CMP may be performed to planarized top surfaces of theworkpiece 200. In some embodiments, the metal fill layer 226 may includetantalum nitride (TaN), nickel silicide (NiSi), cobalt silicide (CoSi),molybdenum (Mo), copper (Cu), tungsten (W), aluminum (Al), nickel (Ni),cobalt (Co), zirconium (Zr), platinum (Pt), ruthenium (Ru), or otherapplicable materials.

Reference is now made to FIG. 9, which illustrates a chart 400. Chart400 shows drive current (referred to as “DC” in FIG. 9) performance gainof an n-type FinFET in relation to a depth of recess into the STI, whichcorresponds to the recess 2060 in FIG. 4. As described above, becausethe recess 2060 into the first isolation layer 206 makes room for thesecond isolation layer 218 which is later strained by annealing, FIG. 9may also be viewed as charting drive current performance gain of ann-type FinFET device in relation to the volume of strained secondisolation layer 218. FIG. 9 is based on Technology Computer-Aided Design(TCAD) simulation results and illustrates that drive currents (which maybe referred to as I_(on)) can be improved when larger volume of secondisolation layer 218 replaces the first isolation layer 206 and isannealed to be strained. As illustrated in FIG. 9, in some instances,when the STI recess depth is about 60 nm, the drive current of then-type FinFET may increase by about 5%.

Thus, the various embodiments described herein offer several advantagesover the existing art. For example, the semiconductor device of thepresent disclosure includes an n-type device region and a p-type deviceregion. In the n-type device region, a first isolation layer (STI) isrecessed to have a U-shape to make room for a second isolation layer andthe second isolation layer is annealed to become compressively strained.The compressively strained second isolation layer wraps around a finstructure and serves as a stressor structure that exert a tensile stresson a channel region of the fin structure. The tensile stress improvesthe electron mobility in the channel region of the fin in the n-typedevice region, thereby increasing the performance of the n-type device.The same stressor structure is not fabricated in the p-type deviceregion. The compressively strained second isolation layer in the n-typedevice region is an effective stressor structure and is less likely tosuffer strain relaxation in the course of fabrication of thesemiconductor device. It will be understood that not all advantages havebeen necessarily discussed herein, no particular advantage is requiredfor all embodiments, and other embodiments may offer differentadvantages. Additional embodiments and advantages will be evident tothose skilled in the art in possession of this disclosure.

In one exemplary aspect, the present disclosure is directed to asemiconductor device. The semiconductor device includes a first finincluding a first source/drain region, a second fin including a secondsource/drain region, a first isolation layer disposed between the firstsource/drain region and the second source/drain region, and a secondisolation layer disposed over the first isolation layer. A first portionof the first isolation layer is disposed on sidewalls of the firstsource/drain region and a second portion of the first isolation layer isdisposed on sidewalls of the second source/drain region. A portion ofthe second isolation layer is disposed between the first portion andsecond portion of the first isolation layer.

In some embodiments, the semiconductor device further includes an etchstop layer disposed between the first isolation layer and the secondisolation layer. In some embodiments, the semiconductor device mayfurther include a spacer. The first portion of the spacer is disposedover the first portion of the first isolation layer and a second portionof the spacer is disposed over the second portion of the first isolationlayer. In some implementations, the semiconductor device may furtherinclude an etch stop layer disposed over and in contact with the firstand second portions of the spacer and the first isolation layer. Thesecond isolation layer is disposed over and in contact with the etchstop layer. In some instances, the semiconductor device further includesa substrate. The first and second fins are connected to and extend fromthe substrate. The first isolation layer further includes a bottomportion extending between the first portion and the second portion. Thetop surfaces of the first and second portions have a first heightmeasured from a top surface of the substrate. A top surface of thebottom portion has a second height measured from the top surface of thesubstrate. The first second height is between about 5% and about 50% ofthe second first height. In some embodiments, the first isolation layeris U-shaped. In some implementations, a composition of the firstisolation layer is different from a composition of the second isolationlayer.

In one exemplary aspect, the present disclosure is directed to asemiconductor device. The semiconductor device includes an n-type deviceregion and a p-type device region. The n-type device region includes afirst fin including a first source/drain region, a second fin includinga second source/drain region, a first isolation layer disposed betweenthe first source/drain region and the second source/drain region, and asecond isolation layer disposed over the first isolation layer. Thep-type device region includes a third fin including a third source/drainregion, a fourth fin including a fourth source/drain region, and thefirst isolation layer disposed between the third source/drain region andthe fourth source/drain region. In the n-type device region, a portionof the second isolation layer extends into the first isolation layerbetween the first and second source/drain regions.

In some embodiments, the first isolation layer in the n-type deviceregion is U-shaped. In some embodiments, a top surface of the firstisolation layer in the p-type device region is substantially planar. Insome implementations, the semiconductor device may further include anetch stop layer disposed between the first isolation layer and thesecond isolation layer. In some instances, the first fin has a lowerportion in contact with the first isolation layer and the second fin hasa lower portion in contact with the first isolation layer. In addition,a portion of the first isolation layer and the portion of the secondisolation layer that extends into the first isolation layer are disposedbetween the lower portion of the first fin and the lower portion of thesecond fin. In some embodiments, a portion of the etch stop layer isdisposed between the lower portion of the first fin and the lowerportion of the second fin. In some implementations, the n-type deviceregion further includes a spacer. The first fin has an upper portionover the lower portion the first fin and the second fin has an upperportion over the lower portion of the second fin. The spacer is incontact with the upper portion of the first fin and the upper portion ofthe second fin. In some instances, the third fin has a lower portion incontact with the first isolation layer and the fourth fin has a lowerportion in contact with the first isolation layer. The lower portion ofthe third fin and the lower portion of the fourth fin are separated onlyby the first isolation layer.

In another exemplary aspect, the present disclosure is directed to amethod. The method includes providing a workpiece. The workpieceincludes a first fin in an n-type device region, a second fin in thep-type device region, and a dielectric layer. The first fin extendsthrough a first isolation layer and includes a first source/drainregion. The second fin extends through the first isolation layer andincludes a second source/drain region. The dielectric layer is disposedover the first fin, the second fin and the first isolation layer. Themethod further includes etching the first isolation layer in the n-typedevice region to form a recess in the first isolation layer in then-type device region; and depositing a second isolation layer over thefirst isolation layer and in the recess. A composition of the firstisolation layer is different from a composition of the second isolationlayer.

In some embodiments, the method may further include depositing an etchstop layer before the depositing of the second isolation layer. In someembodiments, the method may further include annealing the secondisolation layer to impart a tensile stress on the first fin. In someimplementations, the providing of the workpiece includes depositing aspacer material over the first fin, the second fin and the firstisolation layer; and recessing the spacer material deposited over topsurfaces of the first fin, the second fin and the first isolation layerto form spacers in contact with sidewalls of the first and second fins.The etching of the first isolation layer to form the recess in the firstisolation layer in the n-type device region includes using the spacersas an etch mask. In some implementations, the method further includesdepositing an etch stop layer over the etched first isolation layer andwithin the recess in the n-type device region.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure. For example, by implementing different thicknessesfor the bit line conductor and word line conductor, one can achievedifferent resistances for the conductors. However, other techniques tovary the resistances of the metal conductors may also be utilized aswell.

What is claimed is:
 1. A semiconductor device, comprising: a first finincluding a first source/drain region; a second fin including a secondsource/drain region; a first isolation layer disposed between the firstsource/drain region and the second source/drain region; a secondisolation layer disposed over the first isolation layer; and an etchstop layer disposed between and interfacing with the first isolationlayer and the second isolation layer such that the first isolation layeris prevented from interfacing with second isolation by the etch stoplayer, wherein a first portion of the first isolation layer is disposedon sidewalls of the first source/drain region and a second portion ofthe first isolation layer is disposed on sidewalls of the secondsource/drain region, wherein a portion of the second isolation layer isdisposed between the first portion and second portion of the firstisolation layer.
 2. The semiconductor device of claim 1, furthercomprising a spacer, wherein a first portion of the spacer is disposedover the first portion of the first isolation layer and a second portionof the spacer is disposed over the second portion of the first isolationlayer.
 3. The semiconductor device of claim 2, wherein the etch stoplayer physically contacts the first and second portions of the spacerand the first isolation layer, wherein the second isolation layer isdisposed over and in physical contact with the etch stop layer.
 4. Thesemiconductor device of claim 1, further comprising a substrate, whereinthe first and second fins are connected to and extend from thesubstrate, wherein the first isolation layer further includes a bottomportion extending between the first portion and the second portion,wherein top surfaces of the first and second portions have a firstheight measured from a top surface of the substrate, wherein a topsurface of the bottom portion has a second height measured from the topsurface of the substrate, wherein the second height is between about 5%and about 50% of the first height.
 5. The semiconductor device of claim1, wherein the first isolation layer is U-shaped.
 6. The semiconductordevice of claim 1, wherein a composition of the first isolation layer isdifferent from a composition of the second isolation layer.
 7. Thesemiconductor device of claim 1, wherein the first source/drain regionincludes a first source/drain feature extending to a first height, andwherein the portion of the second isolation layer further extendsbetween the first and second source/drain regions to a second heightthat is greater than the first height of the first source/drain feature.8. A semiconductor device, comprising: an n-type device regioncomprising: a first fin disposed on a substrate and including a firstsource/drain region, the first source/drain region including a firstsource/drain feature extending to a first height over the substrate, asecond fin disposed on the substrate and including a second source/drainregion, a first isolation layer disposed between the first source/drainregion and the second source/drain region, and a second isolation layerdisposed over the first isolation layer; and a p-type device regioncomprising: a third fin disposed on the substrate and including a thirdsource/drain region, a fourth fin disposed on the substrate andincluding a fourth source/drain region, and the first isolation layerdisposed between the third source/drain region and the fourthsource/drain region, wherein, in the n-type device region, a portion ofthe second isolation layer extends into a recess defined by the firstisolation layer between the first and second source/drain regions,wherein the portion of the second isolation layer further extendsbetween the first and second source/drain regions to a second heightthat is greater than the first height of the first source/drain feature.9. The semiconductor device of claim 8, wherein the first isolationlayer in the n-type device region is U-shaped.
 10. The semiconductordevice of claim 8, wherein a top surface of the first isolation layer inthe p-type device region is substantially planar.
 11. The semiconductordevice of claim 8, further comprising: an etch stop layer disposedbetween the first isolation layer and the second isolation layer. 12.The semiconductor device of claim 11, wherein the first fin has a lowerportion in physical contact with the first isolation layer and thesecond fin has a lower portion in physical contact with the firstisolation layer, wherein a portion of the first isolation layer and theportion of the second isolation layer that extends into the firstisolation layer are disposed between the lower portion of the first finand the lower portion of the second fin.
 13. The semiconductor device ofclaim 12, wherein a portion of the etch stop layer is disposed betweenthe lower portion of the first fin and the lower portion of the secondfin.
 14. The semiconductor device of claim 12, wherein the n-type deviceregion further comprises a spacer, wherein the first fin has an upperportion over the lower portion the first fin and the second fin has anupper portion over the lower portion of the second fin, wherein thespacer is in physical contact with the upper portion of the first finand the upper portion of the second fin.
 15. The semiconductor device ofclaim 8, wherein the third fin has a lower portion in physical contactwith the first isolation layer and the fourth fin has a lower portion inphysical contact with the first isolation layer, wherein the lowerportion of the third fin and the lower portion of the fourth fin areseparated only by the first isolation layer.
 16. A method, comprising:providing a workpiece, the workpiece comprising: a first fin in ann-type device region, wherein the first fin extends through a firstisolation layer and includes a first source/drain region, a second finin a p-type device region, wherein the second fin extends through thefirst isolation layer and includes a second source/drain region, and adielectric layer over the first fin, the second fin and the firstisolation layer; etching the first isolation layer in the n-type deviceregion to form a recess in the first isolation layer in the n-typedevice region; depositing a second isolation layer over the firstisolation layer and in the recess, wherein a composition of the firstisolation layer is different from a composition of the second isolationlayer; and annealing the second isolation layer to impart a tensilestress on the first fin.
 17. The method of claim 16, further comprisingdepositing an etch stop layer before the depositing of the secondisolation layer.
 18. The method of claim 16, wherein the providing ofthe workpiece comprises: depositing a spacer material over the firstfin, the second fin and the first isolation layer; and recessing thespacer material deposited over top surfaces of the first fin, the secondfin and the first isolation layer to form spacers in physical contactwith sidewalls of the first and second fins, wherein the etching of thefirst isolation layer to form the recess in the first isolation layer inthe n-type device region comprises using the spacers as an etch mask.19. The method of claim 16, further comprising depositing an etch stoplayer over the etched first isolation layer and within the recess in then-type device region.
 20. The method of claim 16, wherein the secondisolation layer includes a dielectric material having function groups,and wherein the annealing of the second isolation layer to impart thetensile stress on the first fin includes shrinking the second isolationlayer by the functional groups of the dielectric material decompose orcondense to produce volatile compounds that leave the dielectricmaterial during the annealing of the second isolation layer.